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Pulmonary embolism. Coloured axial computed tomography (CT) scan of a pulmonary embolism. A large embolus (blood clot) is present in the left main pulmonary artery (dark red). The clot often originates in the deep veins of the legs and travels through the venous system to the lungs, where it becomes lodged. Symptoms include acute shortness of breath, chest pain, rapid heart and respiratory rates, or sudden death. Pulmonary embolism can lead to lung infarction, the death of an area of lung deprived of blood and oxygen. Treatment is with anti-coagulant or thrombolytic drugs, or surgery.